Beryllium oxide (BeO), also known as beryllia, is an
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistr ...
with the
formula BeO. This colourless solid is a notable electrical insulator with a higher thermal conductivity than any other non-metal except
diamond, and exceeds that of most metals.
As an
amorphous solid
In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal.
Etymology
The term comes from the Greek ''a'' ("wi ...
, beryllium oxide is white. Its high melting point leads to its use as a
refractory
In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase, ...
material. It occurs in nature as the mineral
bromellite
Bromellite, whose name derives from the Swedish chemist Magnus von Bromell (1670–1731), is a white oxide mineral, found in complex pegmatitic manganese-iron deposits, but is more frequently made synthetically. This is a rare mineral to encounte ...
. Historically and in materials science, beryllium oxide was called glucina or glucinium oxide, owing to its sweet taste.
Preparation and chemical properties
Beryllium oxide can be prepared by
calcining
Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), gener ...
(roasting)
beryllium carbonate, dehydrating
beryllium hydroxide
Beryllium hydroxide, Be(OH)2, is an amphoteric hydroxide, dissolving in both acids and alkalis. Industrially, it is produced as a by-product in the extraction of beryllium metal from the ores beryl and bertrandite. The natural pure beryllium hydro ...
, or igniting metallic
beryllium
Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form ...
:
:BeCO
3 → BeO + CO
2
:Be(OH)
2 → BeO + H
2O
:2 Be + O
2 → 2 BeO
Igniting beryllium in air gives a mixture of BeO and the nitride
Be3N2.
Unlike the oxides formed by the other Group 2 elements (alkaline earth metals), beryllium oxide is
amphoteric
In chemistry, an amphoteric compound () is a molecule or ion that can react both as an acid and as a base. What exactly this can mean depends on which definitions of acids and bases are being used.
One type of amphoteric species are amphiprot ...
rather than basic.
Beryllium oxide formed at high temperatures (>800 °C) is inert, but dissolves easily in hot aqueous
ammonium bifluoride
Ammonium hydrogen fluoride is the inorganic compound with the formula or . It is produced from ammonia and hydrogen fluoride. This colourless salt is a glass- etchant and an intermediate in a once-contemplated route to hydrofluoric acid.
Structu ...
(NH
4HF
2) or a solution of hot concentrated
sulfuric acid (H
2SO
4) and
ammonium sulfate
Ammonium sulfate (American English and international scientific usage; ammonium sulphate in British English); (NH4)2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen a ...
((NH
4)
2SO
4).
Structure
BeO crystallizes in the hexagonal
wurtzite structure, featuring tetrahedral Be
2+ and O
2− centres, like
lonsdaleite
Lonsdaleite (named in honour of Kathleen Lonsdale), also called hexagonal diamond in reference to the crystal structure, is an allotrope of carbon with a hexagonal lattice, as opposed to the cubical lattice of conventional diamond. It is found ...
and w-
BN (with both of which it is
isoelectronic). In contrast, the oxides of the larger group-2 metals, i.e.,
MgO
Magnesium oxide ( Mg O), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ion ...
,
CaO Cao or CAO may refer to:
Mythology
*Cao (bull), a legendary bull in Meitei mythology
Companies or organizations
* Air China Cargo, ICAO airline designator CAO
* CA Oradea, Romanian football club
*CA Osasuna, Spanish football club
* Canadian Ass ...
,
SrO,
BaO, crystallize in the cubic
rock salt motif with octahedral geometry about the dications and dianions.
At high temperature the structure transforms to a tetragonal form.
In the vapour phase, beryllium oxide is present as discrete
diatomic molecules. In the language of
valence bond theory, these molecules can be described as adopting ''sp'' orbital hybridisation on both atoms, featuring one
σ (between one ''sp'' orbital on each atom) and one
π bond
In chemistry, pi bonds (π bonds) are covalent chemical bonds, in each of which two lobes of an orbital on one atom overlap with two lobes of an orbital on another atom, and in which this overlap occurs laterally. Each of these atomic orbit ...
(between aligned ''p'' orbitals on each atom oriented perpendicular to the molecular axis). Molecular orbital theory provides a slightly different picture with no ''net'' sigma bonding (because the 2''s'' orbitals of the two atoms combine to form a filled sigma bonding orbital and a filled sigma* anti-bonding orbital) and two pi bonds formed between both pairs of ''p'' orbitals oriented perpendicular to the molecular axis. The sigma orbital formed by the ''p'' orbitals aligned along the molecular axis is unfilled. The corresponding ground state is ...(2sσ)
2(2sσ*)
2(2pπ)
4 (as in the isoelectronic C
2 molecule), where both bonds can be considered as dative bonds from oxygen towards beryllium.
Applications
High-quality crystals may be grown
hydrothermally, or otherwise by the
Verneuil method
The Verneuil method (or Verneuil process or Verneuil technique), also called flame fusion, was the first commercially successful method of manufacturing synthetic gemstones, developed in the late 1883 by the French chemist Auguste Verneuil. It i ...
. For the most part, beryllium oxide is produced as a white amorphous powder,
sintered
Clinker nodules produced by sintering
Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction.
Sintering happens as part of a manufacturing ...
into larger shapes. Impurities, like carbon, can give a variety of colours to the otherwise colourless host crystals.
Sintered
Clinker nodules produced by sintering
Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction.
Sintering happens as part of a manufacturing ...
beryllium oxide is a very stable
ceramic. Beryllium oxide is used in rocket engines and as a transparent
protective over-coating on
aluminised telescope mirrors.
Beryllium oxide is used in many high-performance
semiconductor parts for applications such as radio equipment because it has good
thermal conductivity while also being a good electrical insulator. It is used as a filler in some thermal interface materials such as
thermal grease
Thermal paste (also called thermal compound, thermal grease, thermal interface material (TIM), thermal gel, heat paste, heat sink compound, heat sink paste or CPU grease) is a thermally conductive (but usually electrically insulating) chemi ...
.
Some
power semiconductor device
A power semiconductor device is a semiconductor device used as a switch or rectifier in power electronics (for example in a switch-mode power supply). Such a device is also called a power device or, when used in an integrated circuit, a power IC. ...
s have used beryllium oxide ceramic between the
silicon chip and the metal mounting base of the package to achieve a lower value of
thermal resistance than a similar construction of
aluminium oxide. It is also used as a structural
ceramic for high-performance microwave devices,
vacuum tubes,
magnetrons, and
gas laser
A gas laser is a laser in which an electric current is discharged through a gas to produce coherent light. The gas laser was the first continuous-light laser and the first laser to operate on the principle of converting electrical energy to a laser ...
s. BeO has been proposed as a
neutron moderator for naval marine high-temperature
gas-cooled reactor
A gas-cooled reactor (GCR) is a nuclear reactor that uses graphite as a neutron moderator and a gas (carbon dioxide or helium in extant designs) as coolant. Although there are many other types of reactor cooled by gas, the terms ''GCR'' and to a l ...
s (MGCR), as well as NASA's
Kilopower nuclear reactor for space applications.
Safety
BeO is
carcinogen
A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substa ...
ic in powdered form and may cause a chronic allergic-type lung disease
berylliosis
Berylliosis, or chronic beryllium disease (CBD), is a chronic allergic-type lung response and chronic lung disease caused by exposure to beryllium and its compounds, a form of beryllium poisoning. It is distinct from acute beryllium poisoning, wh ...
. Once fired into solid form, it is safe to handle if not subjected to machining that generates dust. Clean breakage releases little dust, but crushing or grinding actions can pose a risk.
References
External links
Beryllium Oxide MSDS from American Beryllia
{{DEFAULTSORT:Beryllium Oxide
Beryllium compounds
Oxides
IARC Group 1 carcinogens
Ceramic materials
Nuclear technology
II-VI semiconductors
Wurtzite structure type